The thymus gland is described further under the lymphatic system. This gland is located posterior to the sternum, in the mediastinum. It is large in infants and children; however, it reduces in size after puberty. The thymus is important for immunity and contains lymphocytes in various stages of develop-ment. Lymphocytes processed in the thymus, known as T lymphocytes, migrate to various parts of the body.
The gland is considered to have endocrine func-tion because it secretes many hormones (thymosins) that stimulate the synthesis and development of lym-phocytes.